As related from an article entitled, Border Merchants, in "The Paisano," a newspaper publication from the National Park Service we picked up at the entry station to Big Bend National Park...

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"Mexican Nationals may approach you from across the river to purchase souvenir items (walking sticks, bracelets, crafts, etc,) If you agree to look at/or purchase their items and the Mexicans cross the river, they may be arrested for being in the U.S. illegally. They will be held until deported back to Mexico through Presidio (100 miles away). Mexican merchants will be arrested for illegal commercial operations which may result in a fine and/or additional incarceration while awaiting adjudication prior to deportation.

Items purchased will be considered contraband and seized by officers when encountered..."